Catalysts for converting hydrocarbons

ABSTRACT

A CATALYST WHICH COMPRISES A CARRIER, FROM 0.005 TO 1% OF PLATINUM AND FROM 0.005 TO 1% OF IRIDIUM WITH RESPECT TO THE CARRIER WITH A SUBSTNTIALLY HOMOGENOUS DISTRIBUTIN OF PLATINUM AND IRIDUM. THIS CATALYST MAY BE USED FOR CONVERSION, FOR EXAMPLE BY REFORMING OF HYDROCARBOSNS. ITS PROCESS OF MANUFACTURE COMPRISES THE USE OF AN AQUEOUS SOLUTION OF BOTH PLATINUM AND IRIDUM COMPOUNDS AND AN AMINOALCHOL AT A PH NOT IN EXCESS OF 4.

US. Cl. 252-466 PT 11 Claims ABSTRACT OF THE DISCLOSURE A catalyst which comprises a carrier, from 0.005 to 1% of platinum and from 0.005 to 1% of iridium with respect to the carrier with a substantially homogeneous distribution of platinum and iridium. This catalyst may be used for conversion, for example by reforming, of hydrocarbons. Its process of manufacture comprises the use of an aqueous solution of both platinum and iridium compounds and an aminoalcohol at a pH not in excess of 4.

This invention relates to a new catalyst containing platinum and iridium, said metals being regularly distributed in the carrier.

This catalyst may be used for reforming hydrocarbons or in any other conversion reaction such as hydrogenation, dehydrogenation or isomerisation of hydrocarbons.

The regular distribution of the active elements of the catalyst in the carrier results from a particular method for manufacturing the catalyst. It has been found that the manufacture of catalysts containing platinum and iridium on a carrier is attended with difliculties in view of the selective adsorption which occurs when the carrier is impregnated with the solution containing the active elements to be introduced therein.

For example, when manufacturing a reforming, dehydrogenation, isomerisation or hydrogenation catalyst, the conventionally used ammonium salts, such as ammonium chloroplatinate, ammonium chloroiridate or other ammonium salts, do not inhibit the chromatography effects which result in metal agglomeration leading to catalysts which quickly lose their activity. This is the case of, for example, the platinum/iridium catalyst of US. Pat. 2,848,377, which is manufactured according to conventional methods.

This chromatographic effect, which already appears when only one active element is deposited, is quite detrimental when platinum and iridium are both to be deposited in homogeneous manner.

It has been found that the quality and the homogeneity of this impregnation may be substantially improved by using, as impregnation solution, an aqueous solution of platinum and iridium compounds containing an aminoalcohol having, for example 1 to 6 OH groups and 1 to 6 amine groups and preferably 2 to 20 carbon atoms per molecule, the pH of the solution being at most 4 and preferably at least 1, or better, 1.5, equivalent to pH ranges of 1-4 and 1.5-4, respectively.

Typical amino-alcohols are ethanolamine, propanolamines, butanolamines, diethanolamine, 2,2-diamino-l,3- propanediol, 2,2,3-triamino-1-propanol or triethanolamine. Ethanolamine is the preferred amino-alcohol.

As a rule, to obtain a homogeneous impregnation of the active elements on the carrier, there is preferably used from 0.05 to 1.5 moles of amino-alcohol per mole of the platinum and iridium compounds considered as chloroplatinic and chloroiridic acids.

"United States Patent The carrier may be silica, alumina, magnesia, aluminasilica or any other solid material having suitable textural and structural properties.

Typical platinum and iridium compounds are chloroplatinic acid, platinum tetrachloride, bromoplatinic acid, chloroiridic acid, iridium tetrachloride, ammonium compounds such as ammonium chloroplatinate and ammonium chloroiridate.

Platinum and iridium may be used in individual amounts of 0.005 to 1% by weight with respect to the carrier. Iridium is preferably used in an amount of 0.005 to 0.1% and particularly 0.01 to 0.09%. Preferred catalysts contain about 0.35% or 0.2% platinum and 0.08% iridium. The catalyst may contain 0 to 15% of halogen, for example fluorine or chlorine, and preferably, 0.2 to 3% b.w. with respect to the carrier.

The catalysts of this invention, containing platinum and iridium, may be used inconventional reactions, for example reforming, isomerization, dehydrogenation, hydrogenation and the like.

The homogeneity of the impregnation on the carrier may be controlled with the well-known Castaing microanalyser which has been the object of the Tubingen Congress (Germany, Sept. 13-16, 1968). This microanalyser is described in vol. XVII of Chemical Analysis (Electron Probe Microanalysis by L. S. Birks) published in 1963 by Interscience Publishers (New York/London).

The Castaing microanalyser may be used to examine the plane cross section of a catalyst grain with X-rays, and to determine the superficial distribution of the considered metal elements, Pt and Ir. There is obtained a diagram showing the distribution of each element along an axis determined on the surface by recording the X-spectrophotometer signal during the scanning along this axis.

There is given hereafter the operating directions with respect to alumina, although the same directions apply to the other carriers.

MANUFACTURE OF THE SAMPLES Agglomerates of catalyst (the size and the shape of the agglomerates is without influence on the method of Castaing. For example, the agglomerates may have their larger dimension between 0.2 and 50 mm.; the other dimensions being at least 0.1 mm.), are finely polished with a diamond along plane sections and observed by reflection microscopy and analysed by points, at the micron scale, in an electronic microanalyser.

Before polishing, they had been coated with a resin polymerisable at low temperature, by groups of ten in the same manufactured series.

METALLISATION It has been found necessary to coat the thus prepared surfaces with a metal, to remove the electric charges which would accumulate at the impact point and would deviate the analyser, and to dissipate the heat thus avoiding the burning of the target. It has been found that a copper layer of 200 A., obtained by metallisation in vacuo was a convenient compromise for a qualitative inspection: if the layer is too thin, it does not work, if it is too thick, it does not allow a proper micrographic inspection.

GENERAL CONDITIONS OF INSPECTION A 30K volts acceleration voltage has been selected to obtain a proper excitation of the L rays of platinum and iridium; it is better that the matrix (alumina) has a low atomic N since, at this high voltage, it gives only a reasonable noise.

It has been found that the detection sensitivity was the same with either platinum or iridium, and that the emission rays used for the analysis did not interfere with one another.

On the other hand, in view of the known values of the massic absorption coefficients of platinum and iridium in each other, and those of platinum and iridium in alumina, it may be deduced that the detection sensitivity for one element cannot be modified by the presence of the other element (internal absorption).

Finally the current in the analyser has been selected as high as possible (10' A.) so as to obtain the highest sensitivity.

DIRECTIONS OF USE With a fixed beam of electrons, the sample has been moved along a diameter, and, for one given element, the relative concentrations have been recorded as a function of the distance. The sample has also been examined manually, point by point, in an attempt to discover local enrichments.

For a given catalyst manufacture, these checkings have been carried out on about 10 sections to average the results.

RESULTS It has been found that, when manufacturing a catalyst containing alumina, platinum and iridium according to conventional methods, the two metal elements (platinum and iridium) are mainly present on the edges of the observed section.

If C is the average concentration of a metal element, it has been found that, with catalysts manufactured according to conventional methods, the concentration in at least one point at the periphery of the sample may reach 20C and even 50C, said peripheral zone having a width of about one tenth of the diameter of the sample, which means that about 50 to 60% of the platinum and 50 to 60% of the iridium are inside this peripheral zone.

Conversely, when using the catalyst manufacturing method of this invention, the resulting catalyst has a concentration, in each point of the carrier, from 0.5C to 2C with respect to platinum (preferably from 0.7C to 1.3C and, whenever possible, from 0.8C to 1.2C and from 0.5C to 2C with respect to iridium (preferably from 0.7C to 1.3C and, wherever possible, from 0.8C to 1.2C C and C being the respective average concentrations of platinum and iridium on the carrier.

This invention thus relates to a catalyst which contains a carrier and from 0.005% to 1% of platinum and from 0.005 to 1% of iridium by weight with respect to the carrier, the distribution of platinum and iridium, as determined, for example, with the Castaing microanalyser, being such that, if C and C are the respective average concentrations of platinum and iridium, the platinum concentration at each point of the carrier is from 0.5C to 2C and the iridium concentration at each point of the carrier is from 0.50 to 2C EXAMPLE 1 Manufacture of a reforming catalyst containing 0.35% platinum and 0.09% iridium by weight from alumina having a surface of 240 m. /g. and a porous volume of 57 cc. per gram.

The catalyst has been manufactured either according to the method of this invention (catalyst A) or, by way of comparison, according to the conventional method, without amino-alcohol (catalyst A Manufacture of catalyst A 0.0023 mole of an aqueous solution of mono-ethanolamine has been added under stirring to 100 cc. of a solution of chloroplatinic acid and chloroiridic acid containing 3.5 g. of platinum and 0.91 g. of iridium per liter, i.e. 0.022 mole of acids. The resulting solution of pH 2.5 is added to 100 grams (dry weight) of wet alumina (manufactured by contacting 140 cc. of water with 100 grams of activated alumina, whose characteristics have been given herebefore, for 30 minutes, adding thereto cc. of water containing 5.7 cc. of hydrochloric acid (d.=1.18), and after a contact time of 7 hours, filtering the same). The contact is maintained for 5 hours, the material is thereafter dried at C. for 1 hour and finally activated by heating at 520 C. for 4 hours. The resulting catalyst contains 0.35% of platinum and 0.09% of iridium. C being the average platinum concentration (0.35%) and C the average iridium concentration (0.09% it can be found, with the Castaing analyser, that the platinum and iridium concentrations, at any point of the carrier, are higher than 0.8C and 0.8C respectively, but do not exceed 1.2C and 1.2C respectively.

Manufacture of catalyst A The process is the same as with catalyst A, however without addition of the monoethanolamine solution. 0n the edges of the samples, zones are apparent where the platinum concentrations range up to 20C, and the iridium concentrations up to 40C EXAMPLE 2 The same alumina as in Example 1 is used for manufacturing a catalyst containing 0.6% Pt, 0.03% Ir and 0.5% CI. The catalyst is manufactured as in Example 1, either according to the method of Example 1 (catalyst B), i.e. with 0.9 cc. of an aqueous solution of 2-amino-1- butanol (0.0032 mole) or, by way of comparison, according to the conventional method (catalyst B without amino-alcohol.

The method is that described in Example 1 except that there is used a solution of chloroplatinic acid and chloroiridic acid containing 5.85 g. of platinum and 0.9 g. of iridium per liter (a total of 0.032 mole of these acids), and the amount of butanolamine for catalyst B is about 0.003 mole per 100 ml. of solution. C' being the average platinum concentration (0.6%) and C the average iridium concentration (0.03%) it may be found with the catalyst analyser that:

with catalyst B, at any point of the carrier, the concentrations of platinum and iridium are never higher than 1.2C' and 1.3C' or lower than 0.8C and 0.7C' and with catalyst B zones may be found, on the edge of the samples, where the platinum and iridium concentrations are as high as 20C' and 50C' respectively.

EXAMPLE 3 The catalysts A, A B and B manufactured according to Examples 1 and 2 have been subjected to a heptane test over a long time under severe conditions so as to simulate an accelerated ageing of the catalyst.

Reduction conditions: temperature of 400 C.; duration of 15 hours; hydrogen pressure of 10 kg. per sq. cm.

Reaction conditions:

Temperaaure: 510 C.

Pressure: 10 kg./cm.

Liquid feed rate: cc. per hour Hydrogen-hydrocarbon molar ratio: 4

Hydrogen feed rate: 74 liters per hour Catalyst weight: 20 g.

(Hourly weight of charge per weight of catalyst: 4)

Samples have been collected after one hour and then each 50 hours and finally each 100 hours.

The experimental results are shown in the following table in which there are given:

(1) The percent molar content of light hydrocarbons (C and C taking the losses into account.

(2) and (3) The percent molar content of the C and C in the product.

(4) The ratio iso C /nC (5) The percent molar content of toluene in the product.

(6) The percent molar conversion rate of nC Results of the tests in moles percent Time in 15001! Tolu- Percent n Catalyst hours Light Cu n01 one converted A 1 4s 9 v 3 3. 5 32 99 50 46 9. 5 3. 2 3. 2 26 98 EXAMPLE 4 This example relates to the manufacture of an alumina catalyst containing 0.35% of platinum, 0.05% of iridium and 10% of fluorine. This catalyst has been manufactured according to Example 1, with or without the particular method of this invention, the fluorine being introduced in the form of hydrofluoric acid. The resulting catalyst is used to isomerise a meta-xylene feed charge to para-xylene. The temperature is 430 C., the pressure 12 kg./cm. the hourly weight of charge per weight of catalyst 5 and the molar ratio of hydrogen to the hydrocarbons 5.

With the catalyst manufactured according to this invention, i.e. with an amino-alcohol, the conversion to para- Xylene amounts to 95% of the thermodynamic balance with a yield of xylenes of 99.9% by weight.

The same yield of xylenes of 99.9% by weight is obtained when the catalyst has been manufactured without amino-alcohol; however the conversion to para-xylene was only 90% of the thermodynamic balance (the distribution of the metallic elements of the two catalysts of this example was substantially that of the catalysts A and A EXAMPLE 5 Time Oonver- Selec- (hours) sion rate tivity EXAMPLE 6 Catalysts of transition alumina of 250 m?/ g. area and 0.65 cmfi/g. pore volume, containing 0.3% of platinum and 0.09% of iridium have been manufacturued according to Example 1.

Catalyst D was manufactured with an amino-alcohol and catalyst D without amino-alcohol; the metal elements Percent aromatic hydrocarbons by Time volume in Catalyst ours) the product EXAMPLE 7 This example relates to the manufacture of a reforming catalyst containing 0.35% of platinum and 0.08% of iridium by weight from alumina having a surface of 240 mF/g. and a pore volume of 57 cm. /g.

The catalyst is manufactured either according to the method of the invention (catalyst E) or according to the conventional method (catalyst E without addition of an amino-alcohol.

Manufacture of catalyst E 0.45 ccm. of an aqueous solution of triethanolamine (0.0027 mole) are added to 100 cc. of a solution of chloroplatinic acid and chloroiridic acid containing 3.5 g. of platinium and 0.8 g. of iridium per liter. The resulting solution, of pH 2.5, is added to 100 grams (dry weight) of wet alumina. The latter was manufactured by admixing 100 g. of activated alumina, whose characteristics have been given herebefore, with 140 cc. of water, maintaining the contact for 30 minutes, adding cc. of water with 5.7 cc. of hydrochloric acid (sp. gr.: 1.18), maintaining the contact for 7 hours and filtering.

The contact of the wet alumina with the solution is maintained for 5 hours, then the alumina is filtered, dried forol hour at C. and then activated for 4 hours at 52 C.

The resulting catalyst contains 0.35% platinum and 0.08% iridium. The metal elements are distributed on the carrier substantially as those of catalyst A.

Manufacture of catalyst E The technique is that described with respect to catalyst E, however without solution of triethanolamine. The elements are distributed on the carrier as those of catalyst A Catalysts E and E of Example 7 are used for treating a naphtha having the following characteristics:

Distillation ASTM: 72-170 C. Composition:

Aromatic hydrocarbons: 6.7%% by weight Naphthenic hydrocarbons: 26.8% by weight Parafiinic hydrocarbons: 66.5% by weight Octane number clear research: about 47 Average molecular weight: Specific gravity at 20 C.: 0.733

This naphtha has been passed with recycled hydrogen through each of catalysts E and E under the following conditions:

Pressure: 27 bars Ratio of H to the hydrocarbons (moles): 5. Hourly weight of naphtha per unit weight of catalyst: 3.

The initial temperature is that providing a liquid product of octane number 97. The temperature is progressively increased to maintain the octane number of 97 as soon as it tends to decrease below this figure. The experiment is interrupted when the temperature attains 530 C. Thus, with catalyst E the experiment must be interrupted after 700 hours (the average temperature increase was 4.3 C. per 100 hours); on the contrary, with catalyst E, the experiment is interrupted after 1050 hours (average temperature increase of 2.9 C. per 100 hours). These results show that the present process for manufacturing catalysts yields catalysts more stable than those manufactured according to conventional methods. Catalyst E has proved to be more active than catalyst E since, after 700 hours, with catalyst E the yield by weight of C is 73% while, after 700 hours, with catalyst E, the yield by weight of C is 75.5%.

What is claimed is:

1. In a catalyst comprising a carrier, from 0.005 to 1% of platinum and from 0.005 to 1% of iridium by weight with respect to the carrier the improvement wherein:

the distribution of platinum and iridium on the carrier is substantially homogeneous, said distribution of platinum and iridium, determined with the Castaing microanalyser, being such that, C and C being respectively the average concentrations of platinum and iridium on the carrier, the concentrations of platinum and iridium at any point of the carrier are inthe range of from 05C, to 2C and from 0.5C to 2C respectively.

2. A catalyst according to claim 1, wherein the concentrations of platinum and iridium at any point of the carrier are in the range of from 0.7C to 1.3C and from 0.7C to 1.3C respectively.

3. A catalyst according to claim 1, containing from 0.005 to 1% of platinum and from 0.01% to 0.09% of iridium with respect to the weight of the carrier.

4. A catalyst according to claim 1, containing from 0.005 to 1% of platinum and from 0.01% to 0.09% of iridium with respect to the weight of the carrier.

5. A catalyst as defined by claim 1, wherein said carrier is alumina.

6. A catalyst as defined by claim 2, wherein said carrier is alumina.

7. A catalyst as defined by claim 3, wherein said carrier is alumina.

8. A catalyst as defined by claim 4, wherein said carrier is alumina.

9. A process for manufacturing a catalyst according to claim 1, wherein a carrier is impregnated with an aqueous solution containing both platinum and iridium compounds and an amino-alkanol, said aqueous solution having a pH in the range of 1-4, said amino-alkanol containing 1 to 6 OH groups and 1 to 6 amine groups, the number of carbon atoms of said amino-alkanol being in the range of from 2 to 20, and wherein from 0.05 to 1.5 moles of amino-alkanol are used per mole of the platinum and iridium compounds expressed as chloroplatinic and chloroiridic acids.

10. A process according to claim 9, wherein the aminoalcohol is ethanolamine.

11. A process as defined by claim 9, wherein said carrier is alumina.

References Cited UNITED STATES PATENTS 2,704,281 3/1955 Appell 252-466 PT 2,781,323 2/1957 Hunter 252-460 2,848,377 8/1958 Webb 252-466 PT 3,507,781 4/1970 Spurlock et a1. 252-466 PT 3,554,902 1/1971 Buss 252-466 PT 2,760,940 8/ 1956 Schwarzenbek 252-466 PI 2,777,805 1/1957 Lefrancois et al. 252-472 X DANIEL E. WYMAN, Primary Examiner W. J. SHINE, Assistant Examiner US. Cl. X.R. 

